1. Field of The Invention
The present invention relates generally to a retractor for an automotive seat belt. Specifically, the present invention relates to an automotive seat belt retractor in which extraction of the seat belt is effectively prevented for increasing vehicle safety.
2. Description of The Prior Art
Seat belt retractors are well known which comprise a housing having therein a pretensioner associated with a collision sensor for instantaneously tightening a vehicle occupant's seat belt in the event of collision. The pretensioner commonly comprises a gas cylinder which discharges a gas for rapidly moving a piston within the cylinder, the piston being operatively connected, via a wire, for example, with a spool on which a seat belt is wound for instantaneously tightening the seat belt around the seat occupant.
Further provided within the housing is a clamp for gripping the seat belt, after activation of the pretensioner, for preventing extraction of the seat belt from the housing of the retractor for securely holding a vehicle occupant in the vehicle seat under an emergency condition such as a collision. Such a clamp comprises a fixed portion mounted in the housing and a movable portion which is mounted on a pivotal axis. The seat belt is interposed between the movable and fixed portions of the clamp such that when the pretensioner is activated, the spool winding the belt is moved in the winding direction for tightening the seat belt, then, according to inertial force of a thus restrained vehicle occupant against the seat belt, a free end of the movable portion is caused to rotate, on arm portions attached thereto, in the direction of the fixed portion of the clamp to apply squeezing pressure to the seat belt to prevent extraction thereof. A guide hole may be provided in the housing engaging a projecting end of a roller shaft provided on the free end so as to stabilize movement of the free end. Further, a `return spring` may be provided for maintaining a position of the roller shaft when the retractor is normally used. Thus overall vehicle safety is enhanced by provision of such an arrangement.
One such conventional seat belt retractor arrangement is disclosed in the BMW Repair Manual, 1988.
In such arrangements, the steps of detection of collision by the collision sensor, activation of the pretensioner, tightening of the seat belt, and clamping of the seat belt, occur consecutively and, it is possible that the seat belt may be extracted from the seat belt retractor by a small degree, such as 20-30 mm before effective clamping is established. As the seat belt may be subjected to considerable inertial force during collision, is always desirable to further enhance the locking features of restraint systems such as seat belt retractors.